A common electrode signal (VCOM signal) plays a very important role in a liquid crystal display panel. For the liquid crystal display panel, whether the panel works under an optimal VCOM signal would directly affect display quality of the panel. When the liquid crystal display panel does not work under its optimal Vow signal, brightness and images of the panel will be affected. When the VCOM signal applied to the liquid crystal display panel is greatly deviated from its optimal VCOM signal, sensitive users may feel a flicker of pictures of the liquid crystal display panel, and even feel dizzy. In addition, when the VCOM signal applied to the liquid crystal display panel is greatly deviated from its optimal VCOM signal, the liquid crystal display panel may also have a problem of DC residual.
Therefore, a VCOM signal would be adjusted for each liquid crystal display panel before shipment, so that the liquid crystal display panel works under its optimal VCOM signal. However, such signal adjustment is usually manually finished by operating personnel or automatically finished by machines, which will cause problems such as increased personnel costs, increased machine costs, and capacity losses, and eventually increase production costs, thereby affecting product competitiveness.